Development and characterization of topical formulation for maintenance therapy containing sorbitan monostearate with and without PEG-100-stearate.

OBJECTIVE: Basic therapy is an integral part of the treatment of chronic skin diseases. However, the formulation of skin products should be analysed with respect to the physical stability and tolerance by the patients before applying them to diseased skin. In particular, the suitability of the formulation for use on damaged skin should be taken into consideration so that no exacerbation of the condition is caused. METHODS: The following approach investigated two formulations with the emulsifier sorbitan monostearate and one with the addition of polyethylene glycol 100 stearyl ether. The characterization included rheology, macroscopic and microscopic cream analysis compared to marketed products for basic therapy. Pyranine staining of stratum corneum (SC) and trans-epidermal water loss (TEWL) measurements were performed with ex vivo porcine SC to asses skin barrier function. RESULTS: The rheological characterization showed a gel-like, viscoelastic behaviour of the formulations and a viscosity in the same order of magnitude as the marketed products. Staining with pyranine revealed that skin damage caused by sodium lauryl sulfate was compensated by treatment with the developed formulations. Following the same trend, TEWL results clearly showed decreasing values, which evidence improved skin barrier function. CONCLUSION: In conclusion, the developed sorbitan monostearate formulations can potentially improve deficient skin barrier function as a part of basic therapy of skin diseases and act as a superior alternative to market products comprising a minimum of well-chosen ingredients.

OBJECTIF: la thérapie de base fait partie intégrante du traitement des maladies chroniques de la peau. Cependant, la formulation des produits pour la peau doit être analysée en termes de stabilité physique et de tolérance par les patients avant de les appliquer sur la peau malade. En particulier, il convient de prendre en compte l'adéquation de la formulation à être utilisée sur une peau lésée afin d'éviter toute exacerbation de l'affection. MÉTHODES: l'approche suivante a étudié deux formulations avec l'émulsifiant monostéarate de sorbitane et une autre avec l'ajout d'éther de stéaryle de polyéthylène glycol 100. La caractérisation comprenait la rhéologie, l'analyse macroscopique et microscopique de la crème par rapport aux produits commercialisés pour la thérapie de base. Une coloration à la pyranine de la couche cornée et des mesures de la perte d'eau transépidermique ont été effectuées avec des couches cornées ex vivo de porc pour évaluer la fonction de barrière cutanée. RÉSULTATS: la caractérisation rhéologique a montré un comportement viscoélastique de type gel des formulations et une viscosité du même ordre de grandeur que les produits commercialisés. La coloration à la pyranine a révélé que les lésions cutanées causées par le laurylsulfate de sodium étaient compensées par le traitement avec les formulations développées. Suivant la même tendance, les résultats de la perte d'eau transépidermique ont clairement montré des valeurs en baisse, ce qui témoigne de l'amélioration de la fonction de barrière cutanée. CONCLUSION: en conclusion, les formulations de monostéarate de sorbitane développées peuvent potentiellement améliorer la fonction de barrière cutanée déficiente dans le cadre d'une thérapie de base des maladies de la peau et constituer une alternative supérieure.

Systematic investigation of factors, such as the impact of emulsifiers, which influence the measurement of skin barrier integrity by in-vitro trans-epidermal water loss (TEWL).

Trans-epidermal water loss (TEWL) has been the most widely used method to assess the integrity of the skin barrier and evaluate the irritation potential or the protective properties of topical products for many years. It detects the amount of water that diffuses across the stratum corneum (SC) to the external environment. As one of the most important functions of the skin is to keep water inside the body, an increase in TEWL is used to indicate the skin's impaired barrier function. So far, a variety of commercial instruments are available to measure the TEWL. Their applications mainly focus on the in-vivo TEWL measurements for dermatological examinations or formulation development. Recently, an in-vitro TEWL probe has also been commercially released enabling preliminary tests with excised skin samples. In our study, we first aimed to optimize the experimental procedures for detecting the in-vitro TEWL of porcine skin. Secondly, different kinds of emulsifiers were applied to the skin, including polyethylene glycol-containing emulsifiers (PEG-ylated emulsifiers), sorbitan esters, cholesterol, and lecithin. Sodium lauryl sulfate (SLS) was used as a positive control, and water as a negative control. Based on the findings, we established a protocol for accurately measuring the in-vitro TEWL values, emphasizing that the temperature of the skin sample should be constantly maintained at 32℃. Subsequently, the influences of emulsifiers on the in-vitro TEWL were analyzed. They indicated a significant skin barrier impairment of PEG-20 cetyl ether, PEG-20 stearyl ether, and SLS on in-vitro skin. Furthermore, we interestingly found that there consistently was an alteration of the TEWL values, even after the application of water to the skin. Our findings are of special interest, as the European Medicines Agency (EMA) recommends the use of in-vitro TEWL to determine skin barrier intactness during Franz cell experiments. Thus, this study provides a validated protocol for measuring the in-vitro TEWL and elucidates the impact of emulsifiers on the skin barrier. It also improves the understanding of tolerable variations of in-vitro TEWL and offers recommendations for its use in research.